package com.cloud.code.真题;

import java.util.Arrays;
import java.util.Scanner;

/**
 * 一条长l的笔直的街道上有n个路灯
 */
public class Demo2 {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            int n = scanner.nextInt();
            int len = scanner.nextInt();
            int[] nums = new int[n];
            for (int i = 0; i < n; i++) {
                nums[i] = scanner.nextInt();
            }
            Arrays.sort(nums);
            double max = 0;
            for (int i = 1; i < nums.length; i++) {
                int tem = nums[i] - nums[i - 1];
                if (tem > max) {
                    max = tem;
                }
            }

            if(nums[0]*2 > max){
                max = nums[0]*2;
            }

            if((len - nums[nums.length -1])*2>max){
                max = (len - nums[nums.length -1])*2;
            }

            System.out.printf("%.2f",max/2);
            System.out.println();


        }
    }
}
